This invention relates to a helical scan video tape recorder (VTR), and more particularly to a scan tracking apparatus in which a video reproducing head is deflected to track a video track on a magnetic tape when such VTR produces a still, slow-motion or quick-motion image.
In the special reproduction such as the still image, the slow-motion image and the quick-motion image by using the helical scan VTR, the video reproducing head is deflected vertically along a sawtooth waveform. In this case, it is necessary that the video reproducing head should be controlled to track the center of the video track. Such technique for tracking the video track is disclosed in U.S. Pat. No. 4,151,570. The disclosed technique employs a feed back servo system, in which the video reproducing head is vibrated by an output of a dither oscillator, a frequency modulated RF signal derived from the head is subjected to envelope detection, the resultant output is further subjected to synchronous detection with the output of the dither oscillator, and the synchronous detected output is fed back to the video reproducing head through a head drive amplifier. However, this technique requires the dither oscillator and the servo system which means that the construction of the apparatus is complicated, and a complicated operation is required for regulating the servo system.